1. Field of the Invention
The present invention relates to an apparatus for making an inspection on selected printed circuit or discrete circuit elements on a bare board or printed circuit board with the aid of inspection probes (hereinafter referred to as "probe") to find defects if any, or determine their performances.
2. Description of the Prior Art
In making an inspection on a printed circuit board by eye as to whether all discrete circuit elements are fixed at correct positions it is liable to overlook defective printed circuit boards when eyes get tired. Also, disadvantageously inspection which uses apparatus requires different jigs designed for exclusive use for particular printed boards, and accordingly inspection cost increases. In an attempt to reduce such difficulties some printed circuit board inspection apparatuses have been proposed so that printed circuit boards may be subjected to quick measurements as to: whether they have discrete circuit elements; what kinds of discrete circuit elements are mounted; what functions such discrete circuit elements have; or whether short-circuits or disconnections exist in printed circuit patterns. The results of such measurements are compared with data stored in memories to make a final decision on each discrete circuit element or printed circuit pattern. One example of such inspection apparatus is given in Japanese Patent 57-98869(A).
FIG. 22 is copied from the sole drawing of the Japanese Patent 57-98869(A). The inspection apparatus comprises a first X-Y driving unit 201 and a second X-Y driving unit 202. Each X-Y driving unit has a cross arm 203 or 204 slidable along the stationary beam of the X-Y driving unit 201 or 202. Each cross arm 203 or 204 has a probe 205 or 206 slidably fixed thereto. The first and second X-Y driving units 201 and 202 are connected to a control 209 so that these driving units may be driven according to program.
In operation a pair of probes 205 and 206 are moved above a printed circuit board to a selected coordinate position under the command derived from floppy disks or other recording mediums, and then these probes 205 and 206 are made to contact to selected two points for instance, two legs of a selected discrete element on the printed board. A voltage or current of such a slight magnitude as would cause no harm to the element, is applied to the element to determine the kind, performance or characteristics of the element or detect defects or disconnections if any, in the element or associated circuits. Similar operations and inspections are repeated one after another in the predetermined order.
The length of time involved for inspection (hereinafter referred to as "tact time") is consisted of: the first section in which the probes are raised after completion of the inspection at a selected coordinate position; the second section in which the probes are moved to another selected coordinate position; the third section in which the probes are lowered; and the fourth section in which an inspection is made. The sections other than the fourth section is preferably shortened to possible minimum. The second section is long compared with the other sections, and therefore the loss of time cannot be reduced without shortening the second section.
Also, disadvantageously the freedom with which a probe whose shape is appropriate for the terminal shape of a selected discrete circuit element can be selected and changed is limited because only a single probe can be fixed to a movable arm. The contact by the probes on soldered terminals in printed circuit boards are repeated so many times that the probe tips may be deformed, and accordingly the electrical resistance at contact positions will be changed. This will decrease the accuracy with which an inspection is made. In an attempt to permit inspections to be repeated with same accuracy probes must be changed several times a day. This, however, requires tedious and time-consuming work, and accordingly operating efficiency is lowered.
In case that an inspection is made on an integrated circuit a three-point measurement is often required, but a conventional inspection apparatus cannot meet this request.